Screw anchors are known, comprising a tubular element having a deformable end portion in which longitudinal slits or cuts are obtained, which divide the end portion itself, at the zones concerned by the cuts, into a series of longitudinal anchoring fins; a cone-shaped expansion nut or body engaged onto the end of the end portion; and a screw, which is accommodated inside the tubular element and is adapted to be screwed onto the expansion nut or cone so as to be able to progressively displace it into the end portion of the anchor, so as to cause the radial deformation of the longitudinal fins which, by spreading outwards, determine the anchoring of the anchor to the wall.
Despite their efficiency, the screw anchors of the aforesaid type do not ensure a sufficiently high degree of fastening in some cases.
For this purpose, many efforts have been made during the past years to increase the degree of fastening of the anchors by means of a continuous search of solutions which allow to make the anchoring of the screw anchor to the wall more effective, but many more remain to be done.